The present invention relates to a process for the detoxification of effluents containing cyanide and/or other oxidizable substances utilizing a mixture of hydrogen peroxide and phosphoric acid.
Wastewater from a variety of industrial processes pose a serious problem to the environment because of the presence of components in the wastewater that are harmful to the environment. Effluents from a variety of industrial processes often contain cyanide in various forms, such as simple cyanide and cyanide complexed with other toxic metals. The conversion of these toxic substances into non-toxic materials is of paramount importance before such wastewaters are discharged to the waterways in order to avoid serious damage to the environment, the aquatic life, and adverse impact on public health and safety.
A number of methods are currently available for the treatment of cyanide containing effluents. One of the best among the known methods for treating effluents containing cyanide and heavy metals, such as copper, zinc and nickel, involves the oxidation of cyanide contained in the wastewater with hydrogen peroxide. Heavy metals contained in such wastes are usually removed by precipitation as a part of the overall process. The advantage of hydrogen peroxide over other chemical methods of cyanide destruction is that it adds no new substances to the environment except oxygen and water, unlike other processes which cause additional salt formation and the introduction of those salts into natural waterways.
In the case of effluents arising from ore-processing plants, the waste effluent often takes the form of so-called tailings pulp or slurry, wherein the proportion of solid may be 50% or even higher. In treatment of these pulps by hydrogen peroxide, a relatively large amount of hydrogen peroxide is sometimes required for treatment. In such cases, the economic viability of the detoxification process depends on reducing the consumption of treatment chemicals, especially hydrogen peroxide, as far as possible.
Several methods for reducing the amount of hydrogen peroxide are known. U.S. Pat. No. 4,416,786 assigned to the same assignee as the present application, makes use of accurate measurement of oxidizing agent demand and the control of reagent dosage. U.S. patent application No. 07/183,635, assigned to the same assignee as the present application, involves the removal of magnetic materials before the treatment of pulp, since magnetic components have been found to cause catalytic decomposition of H.sub.2 O.sub.2 and a corresponding increase in consumption.
However, in all of the above processes the consumption of hydrogen peroxide may be too high in many cases involving detoxification of cyanide (simple and metal complexed) in pulps or slurries that contain considerable amounts of solids.
There is, therefore, a need for a process which enables detoxification of cyanide containing effluents, especially a pulp or a slurry containing high amounts of solids, with economically viable amounts of hydrogen peroxide.